The proposed clinical trial will evaluate if a prime dose of the nonavalent HPV vaccine induces persistent and stable immune responses in 9-12 year old girls in the United States over 18 months post-vaccination follow-up period, before deferred booster doses are administered. It will be a prospective, single-arm, open-label, non-randomized, phase IIA trial that will assess immunogenicity of the prime and deferred-booster dosing schedule of the nonavalent prophylactic HPV vaccine among 9-12 year-old girls. A concurrent reference group of 9-12 year old girls receiving a standard dose schedule of the vaccine will also be enrolled for secondary comparison of the immune responses.